Brief Description Of The Prior Art
As concern for pollution of the environment has escalated in recent years, a myriad of regulations imposed by governmental authorities have restricted the methods by which liquids, and especially hydrocarbons, may be legally stored or retained in locations where any type of spillage is apt to contaminate or damage the environment. Such regulations have often included requirements that a redundantcy of containment be provided, whereby if a containing tank is ruptured or caused to spill, a secondary external tank or back up tank or second confining structure of some type will contain or receive the spillage, and keep it from being dispersed into the surrounding area where it may percolate down to contaminate ground water, or destroy surrounding vegetation.
In the case of above-ground storage, requirements have been imposed for placing an earthen containment dike around large metallic storage tanks, so that if the tanks are fractured or ruptured by earthquake, lightning or vandalism, or in some other way, the contents thereof are permitted to leak, such leaked liquids will be contained. The earthen pits thus formed are often required to be lined with a liquid impermeable liner, and the expense of construction of such facilities is high, and sometimes is prohibitively expensive in relation to the value of the objective to be served by placement of the storage tank at that location.
To meet these requirements, a number of systems have been developed which have frequently involved double tanks or double container systems in which one container is placed within another, so that the external container is capable of receiving and containing any liquid which may be spilled or discharged inadvertently from the internal tank. Among such systems which have been proposed, one is that which is shown in Goodhuse, Jr., U.S. Pat. No. 4,638,920. In the Goodhuse, Jr., patent, a cylindrical tank in which a liquid is stored is supported within a trapezoidally-shaped external container, and both are buried in an underground location. It is intended that this underground storage facility shall be placed permanently in the ground, and not moved, once it is constructed and installed at that location. The top of the external tank is closed and access thereto is provided by a removable manhole cover. It is necessary to go inside of the earth-surrounded external tank in order to effect repairs in the event the external tank becomes fractured or ruptured, or in some other way looses its liquid-tight integrity. No provision is made for the removal of the internal tank from the external tank, or for the skidding or other movement of the external tank from one location to another.
In Shelton, Jr., U.S. Pat. No. 4,715,513, a system is disclosed for containing a toxic material within a storage vessel. An external cylindrical jacket is provided which surrounds a toxic material-containing storage vessel, which may also be cylindrical. The external tank or jacket is generally made in two parts which can be joined together as half sections joined at a midplanar location. There is no provision for transporting or skidding the vessels, and in normal use, it is not contemplated that the internal and will be removed from the external jacket.
Wagner U.S. Pat. No. 4,787,772 relates to a generally rectangular containment tank which surrounds a cylindrical storage tank and catches leakage which may develop therefrom. The only thing which appears to support the internal tank within the external tank is the soil, since both are buried under the earth.
A vertically extending system for containing possibly toxic liquids is disclosed in U.S. Pat. No. 4,805,445. Here, the system includes an inner enclosure for containing the liquid to be stored, and an outer enclosure. Both are rigid and leak proof with one mounted inside the other and the two separated by an intermediate space. An upwardly extending neck opens the interior of the inner enclosure to access from above, and conduits extend through this neck to the interior of the inner enclosure for the purpose of charging and discharging the material to be stored in the inner enclosure. The bottom of the inner enclosure is supported above the bottom of the external enclosure by a pair of props or feet.
Durkop U.S. Pat. No. 3,848,765 relates to a double-walled tank. The inner tank is spaced upwardly off of the bottom of the outer tank by means of feet or spacers.
Ershig U.S. Pat. No. 4,871,081 relates to an inner vessel shell which is supported within a concentric outer vessel shell. A grid-lock support system separates the floor 24 of the inner shell from the floor 4 of the outer shell.
Numerous other patents exist which contemplate the provision of concentric tanks or shells with the inner tank being used for liquid storage.